Superconducting Quantum Interference Device (SQUID) arrays have been proposed in the prior art for utilization as radio frequency (RF) magnetic field detectors and as low noise amplifiers for existing primary antenna structures. These arrays of SQUIDs, which can be connected in a plurality of ways, are also known as Superconducting Quantum Interference Filters (SQIFs) or Superconducting SQUID arrays (SQAs). SQAs can consist of Josephson Junctions (JJs), or any other arrays of elements based on superconductivity that provide constructive interference patterns between the elements. Individual Josephson junctions can also be utilized. However, there is no known way to provide a seamless solution for a system consisting of a SQIF chip (i.e., an SQA) in conjunction with supporting structures that can allow for obtaining a calibrated transfer function for the broadband information carried by free space electromagnetic waves.
Being able to accurately detect the magnetic fields that are generated by living organisms' physiological activity with high spatial and temporal resolution can be critical to effectively diagnosing and understanding the physiological activity. For example, very sensitive magnetic field sensors can be used to detect and localize neurological disorders, traumatic brain injuries and understanding human cognition among other use cases is an application for. One such biomagnetic sensing device can be a noninvasive brain imaging technique that measures the magnetic field changes caused by neuronal firing in the brain. This can be a very valuable tool for imaging, because it can be capable of providing sub-millisecond resolution and millimeter cortical accuracy non-invasively.
Similar technologies that measure magnetic fields but use different sensing methods, such as magnetoencephalography (MEG) and Magnetic Resonance Imaging (MRI), are widely accepted as valuable tools in the field of neuroimaging for both research and clinical purposes. A critical advantage of sensing the magnetic fields over other brain imaging techniques, such as EEG, which measures the electric activity, is that magnetic potentials in the brain are not corrupted by muscle movements and physical skull/tissue properties, which can distort cortical electrical signals.
Despite this advantage, MEG and MRI have not increased in popularity to the same extent as other brain imaging modalities, such as electroencephalography (EEG), because the limitations of current MEG systems. These limitations can include rigid sensor placement (which can cause non-optimal signal detection), expensive magnetic shielded rooms to operate effectively, millions of dollars in cost, and lack of portability due to weight and physical form factor.
The intrinsic limitation of current magnetic field biosensors is due to the sensing element, a Superconducting Quantum Interference Device (SQUID), which is typically coupled to a gradiometer and/or magnetometer allowing the detection of magnetic fields as low as 10-15 Tesla (fempto-Tesla) at millisecond time scales. Typically, the SQUIDs utilized in existing equipment can only operate in highly magnetically shielded environments and at very low temperatures that can require the use of liquid helium as a cryogen. However, the capability to produce Superconducting Quantum Arrays consisting of thousands micro-fabricated SQUIDs circuits operating collectively can allow for operation without the need for massive shielded rooms, while maintaining the sensitivity levels of SQUIDs. Another important difference of SQAs is the flux to voltage transfer coefficient. SQAs can exhibit a substantial higher flux-to-voltage transfer coefficient, which can make it feasible to operate the SQA in unshielded situations. Typically, SQAs can provide far superior broadband characteristics than single SQUIDs (up to 100 GHz), with high dynamic range and linearity.
Experiments in the Cryogenic Exploitation of Radio Frequency (CERF) laboratory of the Department of the Navy, Space and Naval Warfare (SPAWAR) Systems Center, Pacific have demonstrated the unshielded operation of SQUID arrays that can detect frequencies from DC to above 100 MHz. Additionally, the CERF laboratory has recently performed the first demonstration of a SQUID array in the open without any shielding. Furthermore, it was also demonstrated the detection of magnetic signals of any amplification in the front or end. The SQUID arrays used in this demonstration were also specifically fabricated for the purpose to demonstrate the capabilities of SQUID arrays to detect small magnetic fields without amplification and shield.
In addition to the relaxation of the shielding requirement, relaxing of operating temperature restrictions can be fundamental to making the SQUID arrays a viable device for medical applications. To do this, high temperature superconductor (HTS) SQUID arrays, or SQUID arrays that can operate in the temperature range of 75 to 100 degrees Kelvin (75-100° K.) can be used. HTS SQUIDs can be adapted to operate at liquid nitrogen temperatures, which can be much higher (relatively speaking), than traditional liquid helium temperatures of other SQUID arrays. Initial tests indicate that HTS SQUIDs can have similar characteristics to their niobium counterpart SQAs (i.e., unshielded operation, high sensitivity, and broadband operation), but with several advantages.
First, because HTS SQUID arrays reduce any complex logistics that are usually associated with the handling of liquid helium. Second, HTS SQUID arrays can considerably reduce the footprint of the equipment, which can further provide for more maneuverability of the device, and can increase the proximity of the sensor to the brain because the requirements to keep nitrogen in its liquid state are much less onerous than for helium. Because typical magnetic signals generated in the human body can be mathematically represented by a typical magnetic dipole, magnetic dipoles can have a magnitude that drops with the inverse of the cube of the distance from the source. This factor is unique to SQUID arrays made of high temperature superconductors and leads to greater sensitivity to the magnetic properties of cortical regions located deeper in the brain once the distance between the sensor and the source of the signal is reduced by a minimum of 10 times resulting in an increase of signal of a minimum of 1000 times. The reduced footprint allows for movement of the device, to place the device much, much closer to the subject for detection of the field
In view of the above, it can be an object of the present invention to provide a device that can be capable of detecting biomagnetic signals. Another object of the present invention can be to provide a MEG device that can detect very small electromagnetic signals emanating from the brain, heart, spinal cord, or other biological systems. Still another object of the present invention can be to provide a device that can detect very small electromagnetic signals emanating from any sized animals, insects, and single or colony of cells in a laboratory set-up. Another object of the present invention can be to provide a device for detecting magnetic field, which has a small magnetic footprint, so that the device can be maneuvered around the subject, instead of vice versa. Still another object of the present invention can be to provide a device that can enable biomagnetic signal detection of brain activity and other physiological measurements at depths, frequencies and time scales far beyond what is currently explored in the fields of Neuroscience using HTS SQUID arrays, in order to provide a more lucid picture of the functionality of biomagnetic pathways in the entire body as well as the brain. Still another object of the present invention can be to provide a device that can be manufactured and deployed in a relatively efficient, cost-effective manner.